As an apparatus for realizing VoIP communications using an existing PBX (Private Branch Exchange) or telephone terminal, there is known a VoIP gateway apparatus for converting a communication signal or a control signal into an IP packet thereby to send out the IP packet to an IP network side and for restoring the communication signal or the control signal from the IP packet received from the IP network side thereby to send out that signal to the PBX or telephone terminal. This VoIP gateway apparatus is described in Patent Document 1, for example.
Patent Document 1: JP-A-2003-298660